Internal combustion engine fuel injection timing refers to the time of delivery of a determined fuel quantity to an internal combustion engine, relative to the engine crank angle. Fuel injection timing may be expressed as an angular offset between an established crank angle, such as the crank angle at an intake valve opening or closing event, and the crank angle at which the fuel delivery begins or ends.
To maintain a desirable engine air/fuel ratio, the amount of fuel delivered is varied as a function of engine operating parameters. For example, the crank angle at which delivery of fuel ends may remain fixed while the crank angle at which delivery of fuel begins may vary as a function of the operating parameters. Such conventional control benefits from a variation in the amount of fuel delivered while holding the timing of delivery substantially constant. In general, conventional fuel delivery timing may be set to a fixed early timing, wherein fuel is injected into an engine intake passage well before a corresponding cylinder intake valve opens to admit the fuel to the cylinder. Such early injection timing increases fuel "residence time", which is the amount of time the fuel has to heat up and vaporize in the area of the hot cylinder intake valve prior to entering the cylinder for combustion. Vaporized fuel generally burns more completely in the cylinder than does liquid fuel. Therefore, up to a timing limit, increased residence time increases the potential for efficient and complete internal combustion engine combustion, increasing engine performance and reducing engine emissions.
Under transient conditions, such as conditions characterized by a rapidly changing engine load, static early injection timing may not be desirable. For example, under decrease transients, such as lift-off transient conditions characterized by a rapidly decreasing engine load, such as when an engine operator commands a rapid decrease in engine speed or output torque, conventional static early injection timing practices lag behind the rapidly reducing fueling needs of the engine, and may require several fueling cycles of delay before properly fueling the engine. Indeed, such conventional practices may not properly fuel the engine until the transient is substantially dissipated due to the early generation and issuance of a fueling command. Specifically, overfueling may occur leading to reduced engine performance.
Likewise, under increase transients, such as tip-in transient conditions characterized by a rapidly increasing engine load, such as when an engine operator commands a rapid increase in engine speed or output torque, early injection timing is preferred for flexibility in control of the amount of fuel delivered and for maximum residence time. For example, it may be desirable for engine response performance, to significantly increase the amount of fuel injected under throttle tip-in transient conditions. Early injection timing will allow for a maximum time for such an increase without overlapping subsequent engine control events, such as the intake valve closing event for the cylinder being fueled. Such valve closing event will effectively truncate the fuel injection event duration, resulting in tip-in underfueling and potential lean hesitation. Throttle tip-in transient conditions at engine idle are particularly sensitive to underfueling and further can require significant increases in the amount of fuel delivered. As such, all but extremely early injection timing values are unacceptable for engine idle tip-in transient conditions. The significant variation in fuel injection timing requirements under different transient conditions makes the conventional static fuel injection timing determination unacceptable. Accordingly, it would be desirable to provide for fuel injection timing control that dynamically adapts to the specific timing needs corresponding to various transient conditions.